|STABLE, DURABLE, RETRIEVABLE
Islets of Langerhans have been implanted into hundreds of diabetics. By far the most common choice is infusion into the portal vein. In the cartoon to the right, the hepatic artery and vein are shown in red and dark blue, and the bile duct in green. The portal vein, light blue, drains the abdominal viscera, bringing all the blood from the intestines (with newly absorbed food, and, incidentally oral drugs) directly to the liver. A syringe is used to infuse isolated islets. They travel with the portal blood and lodge in the liver. They have been shown to be there, functioning, years later.
The size of the sheet prohibits portal infusion. The sheet needs to lie against well vascularized tissue. The cartoon at lest shows the major organs of the abdomen. The sheet could be placed against any of them.
The configuration of the immunoisolation membrane must allow the transplant to be done with minimal surgical risk. At this time our guess is that the omentum, a membrane that wraps around the stomach, will be the site of choice.
The immunoisolation membrane must remain chemically unchanged in the presence of cells and intercellular fluid. For instance, polyethylene glycol is broken down in a few months by the body. Islet Sheets are made of alginates which have been demonstrated to be stable for years in vivo.
The device must be resistant to cracking and breaking from mechanical stress.
The device should be retrievable if the graft fails. The recent history of disease caused by failed breast implants has increased the value of retrievable immune barriers such as the Islet Sheet.
The Islet Sheet
The Islet Sheet is biostable, durable and retrievable. This photo shows an islet sheet just after being sutured to the pancreas of a dog.
This sheet, nine weeks later, remains intact and could be removed from the pancreas by clipping the sutures.